1. Field of the Invention
This invention relates generally to surgical access devices and more specifically to trocars and associated obturators which provide operative access across a body wall of a patient.
2. Discussion of the Prior Art
A trocar is a surgical instrument which is used to provide access across a body wall and into a body cavity, such as the abdominal cavity, in order to facilitate use of surgical instruments in the body cavity. The trocar consists of a hollow cannula which is operatively positioned across the body wall using an obturator. The obturator is removably positioned within the cannula and has a sharpened distal tip which is used to penetrate the body wall. While the sharpened tip of the obturator has facilitated penetration of the body wall, shields have been required to isolate this tip from internal organs which may be present on the other side of the body wall.
Shields of the prior art have taken many different forms. In one case, the shields have been formed as external sleeves advanceable to cover the sharp tip upon penetration of the body wall. In other cases the sharp tip has been shielded by retracting the obturator into the cannula. The shielding function has also been accomplished by forming the sharp tip as a plurality of blades and then providing shields in the form of internal rods disposed between the blades. Representative of this art is U.S. Pat. No. 5,275,583 issued on Jan. 4, 1994 to Lawrence Crainich and entitled Trocar Assembly with Independently Acting Shield Means.
In accordance with the prior art, the sharpened tip of the obturator has been formed from a hollow shaft or a plurality of individual blades. With the shaft configuration, the distal end has been ground to form multiple facets each extending from an axial point proximally and outwardly. The facets of the past have been formed with a planar configuration so that adjacent facets have formed a straight cutting edge where they intersect. Three facets have typically been equally spaced around the 360.degree. distal tip.
A cutting edge has been formed at the intersection of each adjacent pair of the facets. The angle at the sharp cutting edge is equal to the angle between the adjacent facets; one-half of this angle is commonly referred to as the facet angle. In the past, the cutting edges have been formed at an angle not less than the facet angle which in a three-facet embodiment is 60.degree..
Obturators of the blade configuration have been sharpened in a similar manner so that the cutting edges of these blades have also been ground to a facet angle of about 60.degree.. In order to facilitate penetration of the body wall and reduce trauma to the patient, it is desirable to make these cutting edges as sharp as possible.
As noted, it is also desirable to shield the sharpened tip immediately upon penetration of the body wall. Shields of the past have been provided to move from a relatively retracted position to a relatively advanced position in order to cover the sharp tip. Typically the retracted position has required that the shield be displaced from the tip the full length of the facets. Then, in order to cover the distal tip, the shield has been required to move over the full length of the facet. Where this distance has been particularly long, considerable time has been required to fully shield the sharp tip.